The present application relates generally to methods for treating single crystal silicon, and more specifically to cleaning methods for improving surface passivation of textured crystalline silicon for solar cell applications.
Solar cells convert incident radiation such as sunlight into electrical energy. The process of converting light (photons) into electrical energy (voltage) is called the photovoltaic (PV) effect. Solar cells are fashioned from semiconducting materials, which can be monocrystalline, polycrystalline, or amorphous. An exemplary semiconducting material is monocrystalline (i.e., single-crystal) silicon. The performance of a solar cell is measured in terms of its efficiency of converting light energy into electrical energy. The efficiency of the cell is calculated as the ratio of the amount of electric output to the amount of incident light.
A typical solar cell includes a junction of a p-type semiconductor and an n-type semiconductor (p-n junction). In the cell, electron-hole pairs are generated by photons. The electrons and holes migrate respectively to the p-type and n-type semiconductors and accumulate in two opposing contacts. The resulting separation of charge creates a voltage that can be used as a source of electric power.
The efficiency of a solar cell can be increased by providing a roughened (textured) surface that presents a gradual interface between air and the cell. A textured surface scatters incident light at oblique angles, and lengthens its optical path, which effectively traps a greater percentage of light within the cell (i.e., reduces reflective losses).
Chemical processes for texturing silicon introduce surface contamination that if unremoved will adversely affect carrier lifetime and cell efficiency. Thus, efficient and effective cleaning methods for textured silicon used for solar cell applications are desired.